What purpose does the expanded synaptic knob and the ruffled motor end-plate serve?
a) form valleys to accumulate neurotransmitter
b) prevent attachment of synaptic knob to the motor end-plate
c) increase the surface area
d) all of the above
e) none of the above

The correct answer will be option C- increase the surface area.

Explanation:

At the neuromuscular junctions, the axons of the motor-neurons become bulbous at terminals. These bulbous enlargements are known as the synaptic knobs. The synaptic knob is the bulbous enlargements of the axon present at the terminals. These knobs increase the volume of the axon terminals embedded with the ligand-gated channels and accumulation of neurotransmitters in vesicles.

The motor end plate is the region of the muscle fiber which is responsible for initiating the action potential in a muscle. The motor end plate becomes ruffled or shows small folds or clefts to increase the increased surface area for the neurotransmitter to act.

Thus, option C is the correct answer.